Supplemental Patches

Mixins

2 min read

Sometimes, you need fine-grained control over what code is patched into Euphoria Patches. This is where mixins come in. In order to define mixins, you will need

  • a .glsl file to store shader code that will be patched in and
  • a .json file to locate the area where the GLSL code is patched

These files should be placed under the mixins folder.

JSON Format

The following are the parameters specified in the JSON. They are all required.

file - This is the path to the GLSL file in which code should be patched. It should begin with /shader. type - This is one of after, before and replace. This determines how the code is placed with respect to the key. key - This determines the location where the code is patched. code - The path of the GLSL file where the code to be patched is stored.

Examples

Consider the following segment of code from /shaders/program/gbuffers_terrain.glsl.

int subsurfaceMode = 0;
bool noSmoothLighting = false, noDirectionalShading = false, noVanillaAO = false, centerShadowBias = false, noGeneratedNormals = false, doTileRandomisation = true, isFoliage = false;
float smoothnessG = 0.0, highlightMult = 1.0, emission = 0.0, noiseFactor = 1.0, snowFactor = 1.0, snowMinNdotU = 0.0, noPuddles = 0.0, overlayNoiseIntensity = 1.0, snowNoiseIntensity = 1.0, sandNoiseIntensity = 1.0, mossNoiseIntensity = 1.0, overlayNoiseTransparentOverwrite = 0.0, overlayNoiseEmission = 1.0, IPBRMult = 1.0, lavaNoiseIntensity = LAVA_NOISE_INTENSITY, enderDragonDead = 1.0;
vec2 lmCoordM = lmCoord
vec3 normalM = normal, geoNormal = normal, shadowMult = vec3(1.0);
vec3 worldGeoNormal = normalize(ViewToPlayer(geoNormal * 10000.0));
vec3 dhColor = vec3(1.0);
float purkinjeOverwrite = 0.0;

Suppose add a new parameter fogOverride, that can be modified within my terrain shaders. The only way to do this would be using a mixin. We can do this using the following JSON file and GLSL file.

{  
  "file": "/shaders/program/gbuffers_terrain.glsl",  
  "type": "after",  
  "key": "float purkinjeOverwrite = 0.0;",  
  "code": "add_fog_override.glsl"  
}
float fogOverride = 0.0;

This will insert the line float fogOverride = 0.0; just below float purkinjeOverwrite = 0.0;.